1. Field of the Invention
The present invention relates to a spinning apparatus incorporated in a man-made fiber manufacturing machine and an air-gap spinning method, and more specifically to a spinning apparatus provided with a vertical flow type coagulation bath having a novel coagulating liquid flow control unit and an air-gap spinning method of manufacturing acrylic fibers or cellulosic fibers, useful as a carbon fiber precursor by means of the same spinning apparatus.
2. Description of the Prior Art
In general, man-made fiber is manufactured by a melt spinning method, dry spinning method, wet spinning method, etc. according to the properties of the raw materials.
The above-mentioned spinning methods have been improved in turn, and in particular the melt spinning technique has been improved markedly, so that recently various high performance fibers can be manufactured at a high spinning speed.
Although applicable to thermoplastic polymers such as polyamides or polyesters, this melt spinning technique is not applicable to raw materials which will not be melted by heat, such as cellulosic, polyacrylonitrilic polymers, etc. Accordingly, cellulosic or polyacrylonitrilic fiber has been now manufactured in accordance with the wet spinning method, in particular or the dry spinning method.
These dry and wet spinning techniques have not been improved markedly in spite of various efforts, as compared with the melt spinning technique. In the wet spinning technique, in particular, the spinning speed is extremely low because the spinning dope or polymer solution must be directly extruded into a coagulating liquid. To overcome this problem, an air-gap spinning technique has been proposed such that the spinning dope is extruded through a spinneret and then passed through air before being introduced into a coagulating liquid, with the result that the spinning speed has been improved to a considerable extent.
In the above-mentioned air-gap spinning method, it is necessary to pass the extruded liquid-state fiber of spinning dope through the coagulation bath in order to coagulate the liquid-state fiber quickly and uniformly. In more detail, the spinneret must be located over the coagulating liquid; the spinning dope must be extruded downward through the spinneret so that the spinning dope can be coagulated in contact with the coagulating liquid; and the coagulated fiber bundle must be taken out of the coagulation bath thus being problematic in that the spinning apparatus requires a complicated structure and further the workability or the productivity is less than when either the dry or melt spinning method is employed.
In other words, the spinning dope extruded through the spinneret inevitably becomes a mass of dope with gelled skin whenever the dope is extruded, so that the workability at the start of spinning is deteriorated. Here, the start of spinning implies the process from when the spinning dope is extruded through the spinneret into an inert medium (under the condition that the spinning apparatus including the coagulation bath and the first Godet roller operated immediately after the coagulation process are both ready for operation) to when the extruded liquid-state fiber is introduced into the coagulation bath and then the coagulated fiber bundle is taken out of the coagulation bath and is taken up around the first Godet roller. In this spinning start process, the extruded liquid-state fiber is often accumulated at the surface of coagulating liquid, that is, a mass of dope with gelled skin, without being coagulated quickly, is formed.
To improve the spinning start workability, there has been proposed a coagulation bath for air-gap spinning method which is provided with a direction change guide as disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 1-183511. In this proposed method, since the mass of dope with gelled skin produced when the dope is extruded is taken outside the coagulation bath by the direction change guide, the workability can be improved to some extent. However, there exists a shortcoming in that since the coagulated fiber bundle is not yet completely coagulated in the coagulation bath, the filament is subjected to damage due to the friction generated between the filament and the direction change guide. In this method, when the guide is replaced with a rotatable roller, it may be possible to reduce the damage of the coagulated fiber bundle. However, there raises another problem in that the filament is easily wrapped around the roller or the apparatus assumes a rather complicated mechanical structure.
On the other hand, a funnel-type coagulation tube provided with a coagulating liquid flow control unit has been also proposed, as disclosed in Japanese Published Unexamined Patent Application No. 51-35716. According to the method disclosed in this publication the mass of dope with gelled skin produced at the start of spinning is passed through an open valve of the coagulating liquid flow control unit, and the degree of opening of the valve is controlled after the coagulated fiber bundle has been passed through the valve. Further, in this prior art, a few embodiments of controlling the degree of opening of the valve of the coagulating liquid flow control unit have been proposed as follows: (1) the degree of opening of the valve is controlled by use of a shutter similar to that used in a camera, that is, by reducing the diameter of the opening from the circumference toward its center; (2) the degree of opening is controlled by shifting a plate formed with a round notch toward the center of the valve opening; and (3) the degree of opening is controlled by shifting two plates each formed with a round hole, respectively, in two opposite directions, respectively. In any of these embodiments, the degree of opening of the valve is controlled by interrupting the liquid flow, that is, by shifting a control member in the horizontal direction relative to the vertical flow direction of the coagulating liquid.
Accordingly, when the liquid flow is interrupted by shifting the control member in the horizontal direction against the vertical flow direction, there exists a problem in that vortices will be produced in the coagulating liquid in front and to the rear of the opening control member, so that the filament alignment of the semicoagulated-state fiber bundle traveling together with the coagulating liquid is disturbed or the filament is damaged. Therefore, when the filament thus obtained is to be used as a carbon fiber precursor, there arises a problem in not only can it not be possible to obtain a high performance carbon fiber, but also the spreadability of the fiber bundle is not satisfactory due to the deterioration of the filament alignment, in the case where a resin impregnated prepreg sheet is required to be manufactured, for instance.
In addition, the coagulating liquid flow control unit as described above has a complicated structure, and therefore the operability is not satisfactory.